Comparison of remineralization in caries-affected dentin using calcium silicate, glass ionomer cement, and resin-modified glass ionomer cement: an in vitro study
Article information
Abstract
Objectives
This study evaluated the ability of calcium silicate cement (CSC) as a remineralizing agent compared with conventional glass ionomer cement (GIC) and resin-modified GIC (RMGIC) to remineralize artificial caries-affected dentin.
Methods
Twenty-five class V cavities were prepared on extracted human third molars. Twenty teeth underwent artificial caries induction. The remaining five teeth with sound dentin serve as the positive control. The twenty demineralized teeth were subdivided into four groups (n = 5): carious dentin without restoration (negative control [NC]), carious dentin restored with CSC (Biodentine, Septodont), carious dentin restored with GI (Fuji IX, GC Corporation), and carious dentin restored with RMGIC (Fuji II LC, GC Corporation). Following restoration, the specimens were stored in artificial saliva for 7 days. The elastic modulus was evaluated by a nanoindentation test. The mineral composition was analyzed by scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX), and the mineral composition at the dentin-material interface.
Results
CSC had a higher modulus of elasticity compared to GI, RMGI, and NC groups (p < 0.05). Higher calcium and phosphorus content was observed under CSC restorations, as indicated by SEM-EDX examination, which may lead to better remineralization.
Conclusions
Compared to GI and RMGI, CSC showed the best remineralization and mechanical reinforcement in caries-affected dentin, indicating CSC for use in minimally invasive restorative dentistry.
INTRODUCTION
Minimally invasive dentistry focuses on preserving natural tooth structure. It also aims to treat dental caries effectively. A key part of this approach is using restorative materials. These materials not only fill the cavity but also help remineralize caries-affected dentin [1]. The proper adhesion of the restoration is facilitated by the function of an adhesive applied to the bonded interfaces [2]. Adhesive materials are recommended for this approach. These materials enhance the bonding between restorative materials and tooth structure. However, studies have shown that the bonding performance of adhesives to caries-affected dentin is inferior to that observed in sound dentin [3]. This reduced adhesion is attributed to the altered mineral composition and structural disorganization within caries-affected dentin, resulting in a more heterogeneous mineral distribution [4,5].
Materials with remineralizing properties offer a practical option for treating deep carious lesions. They provide an alternative to traditional restorative methods. These materials are called bioactive materials. They can trigger biological responses and help regenerate oral tissues [6]. Glass ionomer cements (GICs) and resin-modified glass ionomer cements (RMGICs) are widely used. They bond chemically to the tooth and can release fluoride. The released fluoride enhances remineralization. However, these materials have limitations in strength and long-term durability [7].
Calcium silicate-based materials (calcium silicate cement, CSC), such as Biodentine (Septodont, Saint-Maur-des-Fossés, France), have emerged as promising alternatives. The material offers bioactivity, biocompatibility, and the ability to induce dentin regeneration through the formation of hydroxyapatite [8]. While previous studies have explored the individual properties of these materials, comparative analyses focusing on their remineralization potential in caries-affected dentin are limited [9,10]. Biodentine is a CSC introduced in 2009, providing an advanced replacement material for dentin. According to the manufacturer’s recommendation [8,11–13], it can be used in restorative treatment as a dentin substitute. It has a similar initial hardness to dentin, with the highest compressive strength compared to other CSCs [14].
A recent study presented comparative findings between two materials, Biodentine and Fuji II LC (GC Corporation, Tokyo, Japan). By using as a dentin replacement material at cervical margins for class II cavity, Biodentine and RMGIC showed a similar result in leakage score [15]. Biodentine offers a promising alternative for caries management due to its effective remineralization properties, which enhance restoration durability and adhesion. Understanding how these materials influence the mechanical properties and mineral content of affected dentin is essential for optimizing restorative strategies.
Therefore, this in vitro study aims to compare the remineralization potential of CSC (Biodentine) with that of conventional GIC (Fuji IX; GC Corporation, Tokyo, Japan) and RMGIC (Fuji II LC) in caries-affected dentin. The assessment involves nanoindentation testing to evaluate mechanical properties and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) to analyze mineral composition at the dentin-material interface.
METHODS
Tooth selection and preparation
This research received ethical approval from the Ethics Committee for Human Study, Srinakharinwirot University (No. SWUEC/X-008/2565). The sample size was determined by using the G*Power program (ver. 3.1.2; Heinrich Heine University of Düsseldorf, Düsseldorf, Germany), based on the pilot study with an effect size of 0.8, an alpha value of 0.05, and a power of 80% which summed to 25 samples. Twenty-five non-carious human third molars with no visible dentin defects or restorations were studied. The teeth were maintained in 0.1% thymol solution at 4°C and used within 6 months of extraction. Thymol solution was renewed every 2 weeks in order to keep a constant antimicrobial action during storage. The acid-resistant nail varnish was applied to the surface of the entire crowns. Then, a cylindrical bur with a diameter of 1 mm was employed to prepare a cavity on the buccal surface for class V cavity dimensioning 4 mm in width, 2 mm in height, and 1.5 mm in depth. The gingival margin is located 1 mm below the cementoenamel junction. A new diamond bur was replaced after every five cavity preparations.
Experimental design
All teeth were randomly divided into five experimental groups (n = 5) including sound cavity in the deionized water (positive control [PC] group), artificial carious lesion without restoration in the deionized water (negative control [NC] group) and artificial carious lesion restored with CSC (Biodentine), GIC (Fuji IX GP EXTRA), and RMGIC (Fuji II LC). All materials were used according to the manufacturer’s instructions.
Artificial caries formation
Artificial caries was simulated using the pH-cycling model in the present experiment. Each specimen was demineralized in a demineralizing solution for 8 hours (10 mL of demineralizing solution containing 2.2 mM CaCl2, 2.2 mM NaH2PO4, 50 mM acetasodium with pH at 4.8) and subsequently remineralized in remineralizing solution (10 mL of remineralizing solution containing 1.5 mM CaCl2, 2.9 mM NaH2PO4, 50 mM KCl with pH at 7.0) for a total of 14 days [16].
Restorative procedure
Artificial carious lesions were restored by CSC, GIC, or RMGIC (n = 5). The material compositions are summarized in Table 1. All materials were used according to the manufacturer’s recommendation. The set samples were then stored in artificial saliva (C8H8O3, 13.2 mM; KCl, 8.4 mM; MgCl2, 0.3 mM; K2HPO4, 4.6 mM; KH2PO4, 2.4 mM; CaCl2, 1.1 mM; and sodium carboxymethyl cellulose, 41.3 mM) adjusted to 7.2 pH for 1 week at room temperature (25⁰C) to simulate the oral environmental condition and to keep their hydration state [17].
Materials used in this study
Modulus of elasticity analysis by the nanoindentation method
All teeth were sectioned longitudinally through the center of the cavities using a low-speed diamond saw (Isomet 1000; Buehler, Lake Bluff, IL, USA). The cut samples were embedded in a filled acrylic resin mold (PalaXpress Ultra; Heraeus Kulzer, Hanau, Germany). The embedded samples were ground with silicon carbide paper (#320, #600, and #1,200) in water and finished with diamond paste (3, 1, and 0.5 µm). The nano-hardness tester (FISCHERSCOPE HM2000; Helmut Fischer GmbH, Sindelfingen, Germany) was used to measure the elastic modulus. The nanoindentor is a diamond four-sided pyramid. The depth of the indentation is 5 μm with a loading resolution of 6 mN. The loading range is for 3 seconds. The diameter of the head of the indentor is 0.4 mm. A Vickers indenter was inserted at the intertubular dentin tubule surface. Distances made from each section were 10, 20, and 30 µm from the axial wall interface of the material and the dentin and 600, 1,200, and 1,800 µm from the cavosurface of the occlusal wall to standardize the test point for all groups and to minimize the experimental error. Thus, each sample contained altogether 18 pressure sites from two segments. The average value of each sample was calculated using the data from the 18 selected points. The average value of each material was the mean of five samples.
Mineral composition analysis
For three samples, quantitative EDX spectroscopy analysis (EDX attached to SEM, JSM-5410LV; JEOL Ltd., Tokyo, Japan) was performed with 10 kV accelerating voltage to determine the mineral content of the dentin.
Statistical analysis
Statistical analysis was performed with IBM SPSS version 20.0 (IBM Corp, Armonk, NY, USA). Normal distribution of the means of modulus of elasticity of all groups was tested using the Shapiro-Wilk test. Differences in modulus of elasticity among the five groups were evaluated by one-way analysis of variance (ANOVA) with a Bonferroni post hoc test for multiple comparisons. A p-value <0.05 was considered significant. Mineral content and demineralization characteristics of dentin were assessed with descriptive analysis.
RESULTS
Dentin mechanical properties by nanoindentation
The comparative analysis of the mean elastic modulus among the five groups of dentin was investigated by one-way ANOVA statistics. The average and standard deviations of the modulus of elasticity are presented in Figure 2. The CSC group had significantly higher values of modulus of elasticity compared with the GIC, RMGIC, and NC groups (p < 0.001). In contrast, the mean elastic modulus of the GIC, RMG, and NC groups showed no statistical differences (p > 0.05).
The mean values of the elastic modulus of each group. The mean values in each bar with the different letters are statistically significantly different (p < 0.05).
Mineral composition of dentin at the interface
In the PC group (Figure 3A), sound dentin showed a high level of calcium and phosphorus. The mineral content of dentin located within a 60 µm range beneath the material in the NC group (Figure 3B) displayed decreased levels of calcium and phosphorus relative to the PC group. The GIC group (Figure 3C) and the RMGIC group (Figure 3D) both exhibited lower levels of calcium and phosphorus in the dentin within a 60 μm range beneath the material, similar to the NC group. Interestingly, in the CSC group (Figure 3E), the levels of calcium and phosphate were higher than in the GIC group, RMGIC group, and NC group.
Scanning electron microscopy images with energy-dispersive X-ray analysis. (A) Positive control group. (B) Negative control group. (C) Conventional glass ionomer cement group. (D) Resin-modified glass ionomer cement group. (E) Calcium silicate cement group.
DISCUSSION
Numerous studies have conclusively reported that remineralization is a significant reparative effect after GIC restorations. The remineralization by GIC restorations is noted by the augmented mineral content in the dentin [18,19]. A recent study of the restorative process with GIC and RMGIC in the dentin was reported. The effect of the restorative materials on dentin mechanical properties was evaluated. Measurements were taken at 7 and 30 days after treatment. An increase in mechanical resistance was observed, especially on day 30, compared to day 1 [20]. Consistent with our study, the mechanical properties of dentin improved in both GIC and RMGIC groups at 7 days. Although there were improvements, these were not significantly different from the NC. Longer study durations may yield varying results among the GIC and RMGIC groups.
In contrast, CSC demonstrated a higher remineralizing potential than GIC and RMGIC in artificial carious lesions, as evidenced by the recovery of dentin’s mechanical strength. Schwendicke et al. [21] stated a similar conclusion that although both cements enhanced mineral gain, it was only CSC that increased the microhardness of carious dentin. Another study using two-photon fluorescence and lifetime imaging techniques demonstrated greater and more extensive mineral deposition in samples filled with CSC compared with those filled with GIC [22]. The efficiency of a biomimetic remineralization system was tested in a previous study. It was reported that the demineralized dentin specimens treated with GIC did not remineralize effectively. It was reported that apatite did not appear in contrast to the CSC group [23].
The results of previous studies and the present study revealed the stronger remineralizing potential of CSC in comparison with GIC. The process of remineralization by GIC groups is based on an ion exchange with dentin. However, CSC induced remineralization via deposition; therefore, it could strengthen dental tissues. CSC played a role in creating mineral crystals that bridge the dentin layer, and the material so-called dentin-mineral infiltration zone [6,11,24]. The results obtained in this study revealed that CSC showed higher levels of calcium and phosphorus mineral content compared with the negative, the GIC and RMGIC groups. The differences between the results can be due to the different pH values of the two materials. The acidic nature of GIC is derived from polyalkenoic acids, in contrast to the alkaline properties of CSC. The alkalinity of CSC is due to the release of hydroxyl ions in the process of its hydration reaction. This increase in pH level may create a beneficial environment where remineralization is able to take place more efficiently inside dentin. This fact leads to the CSC group showing an increased remineralization, resulting in a better quality of the mineral, and an increase in the dentin strength [22].
Assessing the mechanical properties is widely regarded as an effective method for evaluating the quality of dentin remineralization. However, minerals regained should be evaluated by considering both the quantity and quality of the regenerated minerals [25]. Due to the small size of teeth and the natural variations in mineral distribution across different regions of dentin, this study proposed selecting test locations within the intertubular dentin region. Therefore, the nanoindentation test was used in this study [26]. This study utilized the modulus of elasticity to evaluate the mechanical integrity of the remineralized dentin, providing information on its structural strength. Nevertheless, the hardness and modulus of elasticity in dentin exhibit a linear correlation as noted in a previous study [27]. Moreover, the inclusion of EDX provided qualitative information on mineral compositions at the material dentin interface, which has been affected by Biodentine.
There are several methods available to assess the effectiveness of remineralization. In order to facilitate remineralization, specimens must be pretreated as simulated carious lesions by demineralization. This technique allows for accurate assessment of the hardness and modulus of elasticity, which are important indicators of remineralization within the tooth structure. In contrast to standard techniques, nanoindentation has good spatial resolution and can be used to assess the mechanical properties of remineralized regions with minimal preparation. As remineralization involves the re-deposition of minerals into demineralized tissue. Nanoindentation enables a detailed understanding of how these materials contribute to the mechanical strengthening of caries-affected dentin at a microstructural level [28].
In this study, dentin was prepared as caries-affected dentin, characterized by the partial dissolution of minerals. Dentin demineralization simulated through pH cycling appeared to be the most preferred method, as it closely mimics the dynamic process of caries formation in natural teeth. Consequently, the surface hardness closely resembled that of naturally carious dentin [16,29]. However, it is crucial to note that this study was conducted within laboratory settings. Therefore, the artificial carious lesion produced by the pH-cycling method may not fully simulate the appearance of natural carious lesions.
This study compared the mechanical properties of the dentin interface under the restorative materials at a specific time point. The modulus of elasticity of dentin from all groups was compared after one week of storage. The chosen storage time was based on the expectation that all tested materials had undergone remineralization. Prior research indicated that the formation of carbonate apatite reached its maximum at 7 days for Ketac Molar (3M ESPE, Seefeld, Germany) and at 14 days for Riva Light Cure (SDI, Bayswater, VIC, Australia) and Equia Forte (GC Corporation) [30]. However, Kunert et al. [31] demonstrated that remineralization by calcium silicate materials continued to accumulate until 28 days. Further study with different storage times is required to investigate the remineralization pattern of the tested materials.
CONCLUSIONS
Within the limitations of the present in vitro study, CSC presented with better remineralizing capability and mechanical reinforcement when used with caries-affected dentin compared with GIC and RMGIC. The higher value of elastic modulus and more calcium and phosphorus deposition in the CSC group confirmed the application of the CSC. This application could enhance the repair of dentin. These results indicate that CSC can be the restorative material of choice in minimally invasive strategies, especially in deep carious lesions. A long-term study is required to prove its clinical application and longevity.
The cavity design and the exact position of the nanoindentation sites. CEJ, cementoenamel junction.
Notes
CONFLICT OF INTEREST
No potential conflict of interest relevant to this article was reported.
FUNDING/SUPPORT
This study was supported by the Faculty of Dentistry, Srinakharinwirot University, Bangkok, Thailand (research grant number 348/2565).
AUTHOR CONTRIBUTIONS
Conceptualization: Chiaraputt S, Youcharoen K. Data curation, Funding acquisition, Project administration: Chiaraputt S. Formal analysis, Supervision, Validation: Saikaew P, Chiaraputt S. Investigation, Resources: Youcharoen K, Akkaratam O. Methodology: Saikaew P, Chiaraputt S, Youcharoen K. Software, Visualization: Intajak P. Writing - original draft: Youcharoen K, Chiaraputt S. Writing - review & editing: Youcharoen K, Akkaratam O, Intajak P, Saikaew P. All authors read and approved the final manuscript.
DATA SHARING STATEMENT
The datasets are not publicly available but are available from the corresponding author upon reasonable request.